1. Field of the Invention
The present invention relates to cooling devices and methods for acoustic apparatuses and, more specifically, to a cooling device for an acoustic apparatus including a cooling fan that is turned on and off, and adjusted in quantity of airflow in accordance with an apparatus temperature, and a cooling method therefor.
2. Description of the Related Art
For cooling of an electronic apparatus, a cooling fan has been put under control for the purpose. With previous techniques of controlling a cooling fan, the state of a cooling object, i.e., temperature and degree of heat generation, has been extremely simply the factor for turning on and off the cooling fan. That is, when the cooling object is increased in temperature to be higher than a predetermined threshold value, or when the electronic apparatus is put in a state of heat generation, the cooling fan is turned on. On the other hand, when the cooling object is decreased in temperature to be lower than the predetermined threshold value, or when the electronic apparatus is put in a state of no heat generation, the cooling fan is turned off.
With such simple control application over the cooling fan, the cooling effects can be high if the cooling fan is rotated at a high speed during a cooling period. However, if the cooling fan is rotated at a high speed as such for the aim of increasing the cooling effects, fan noise such as rumbling noise and wind noise is generated and often annoys users. Especially with an acoustic apparatus, the sound of a fan turns out to be noise, and thus the performance capabilities thereof are reduced to a considerable degree. For suppressing such fan noise, if an application voltage to the fan or the rotation speed of the fan is reduced, the resulting cooling effects are not enough for the generated amount of heat. This thus increases the apparatus temperature in the acoustic apparatus, and in some cases, this may possibly cause a breakdown of the acoustic apparatus.
As measures against such problems, to reduce the fan noise of a cooling fan as much as possible, a method is proposed to adjust the quantity of airflow of the cooling fan to be in a required value in accordance with the state of a cooling object, i.e., temperature and the degree of heat generation. However, such a method has the following drawbacks. That is, users are annoyed by the sound of change generated when the fan is changed in rotation speed, i.e., when the quantity of airflow is adjusted for the cooling fan. As such, the presence of the fan is made evident, thereby degrading the performance capabilities as an acoustic apparatus.
Patent Document 1 (JP-A-2001-168646) describes a technique of controlling the rotation speed of a fan motor that drives a cooling fan by using three control signals, i.e., an audio output signal level detection signal coming from a comparator in accordance with the output level of a power amplifier, a cabinet temperature detection signal coming from a temperature detection circuit in accordance with the temperature in a cabinet, and a mute signal coming from a mute signal generation circuit. In the technique, a fan motor control circuit increases the rotation speed of the fan motor in response to an output of the audio output signal level detection signal or that of the cabinet temperature detection signal, and forcefully decreases the rotation speed of the fan motor in response to an output of the mute signal. Through such control, the change of rotation speed by the cabinet temperature detection signal takes precedence over the change of rotation speed by any other control signals. Refer also to Patent Document 2 (JP-A-2003-206887).
With such a configuration, when the output of a mute signal is provided in response to the acoustic apparatus being put in the mute state, control is accordingly so exercised that the fan motor is forcefully decreased in rotation speed. That is, when a mute signal is generated, the fan motor is changed in rotation speed. As such, at such speed change, the sound of change resulted therefrom annoys users, thereby making the presence of the fan evident. The technique described in Patent Document 1 is not yet solving the problem of degrading the performance capabilities as an acoustic apparatus.